By way of background, syringes typically include a tubular barrel portion and a plunger having a stopper disposed at one end. The plunger and stopper are inserted into the tubular barrel of the syringe. The stopper portion is typically made of an elastomeric material such as natural or synthetic rubber, which engages an inner surface of the syringe tubular barrel to create a seal that facilitates ejecting a fluid from the syringe when pressure is applied to the plunger.
Traditionally, the inside of the syringe tubular barrels, whether constructed of plastic or glass, and the outside of the stoppers have been lubricated with a silicone oil to reduce the friction between the two parts. By selecting the viscosity and the amount of silicone applied to the inside of the tubular barrel and to the stopper, the friction between them is reduced or adjusted to a desired level.
In conventional syringe fabrication, silicone is applied to the syringe tubular barrels by spraying the silicone oil downwardly into the tubular barrel. This generally results in the entire inside surface of the tubular barrel being covered with silicone. Likewise, the entire stopper typically is coated with silicone oil in a batch process in which a number of stoppers are tumbled together with silicone oil. In both of these processes, the entire inside surface of the syringe barrel and the entire stopper is covered with silicone. In this case, the resultant amount of silicone applied to the syringe barrel and the stopper exceeds what is required to sufficiently reduce the friction between the two parts to a suitable level.
While medical grade silicone oils are not typically harmful, it is desirable to have a medical syringe and method for making the medical syringe that minimizes the amount of silicone used and more effectively and strategically places silicone on the syringe components to reduce the friction between the moving parts of the syringe while eliminating excess lubricant. The advantages of minimizing the amount of silicone which is injected into the body of a patient or subject along with the drug, preventing the leakage of silicone to the outside of the syringe thereby reducing the likelihood that the syringe will slip in the hands of a medical practitioner, and minimizing the interaction between the lubricant (silicone) and the contents of the syringe. Minimizing the interaction between the lubricant and the contents of the syringe is particularly important where syringes are pre-loaded with a particular injectable drug, which may be stored for some time before being administered to a patient.
Accordingly, it is desirable and advantageous to have a medical syringe assembly and method for making a medical syringe assembly in which lubricant is only disposed over a limited area of the syringe in a sufficient amount to provide adequate reduction of friction between the syringe barrel and the stopper.